ARTICLE TOOLS

Abstract

Water quality comprises the physical, chemical, and biological characteristics of a water body. The water body acquires these characteristics from a suite of complex interactions among the water, atmosphere, soils, and lithology. Human activities affect both water quality and quantity. Human activities change land use and land cover, which changes the water balance and usually changes the relative importance of processes that control water quality. Furthermore, most human activities generate waste ranging from gases to concentrated radioactive wastes. Although each issue can be subdivided into a myriad of individual processes or activities, the primary water-quality issues affected by human activities include organic material, trace elements (heavy metals), acidic atmospheric deposition and runoff, salinization, nutrients (primarily nitrogen and phosphorus), pathogenic agents including bacterial pathogens, enteric viruses, and protozoans, suspended sediment, oil and grease, synthetic organic compounds, thermal pollution, exotic and invasive species, pesticides and herbicides, and radioactivity. In addition to the various issues, each human activity has a potential cyclical and cascading effect on water quality and quantity along hydrologic pathways. The degradation of water quality in one part of a watershed can have negative effects on users downstream; the timescale of effects is determined by the residence time of that substance along various hydrological pathways. An extremely important factor is that substances added to the atmosphere, land, and water generally have relatively long timescales for removal or cleanup. The nature of the substance, including its affinity for adhering to soil and its ability to be transformed, affect the mobility and the timescale for the removal of the substance and its effects on water quality, for example, biota.